An EEG signal from a healthy adult contains clinically relevant frequencies in t

Question

An EEG signal from a healthy adult contains clinically relevant frequencies in the range of 0 to 45 Hz. The frequency bands are generally grouped as delta (0.5-4 Hz), theta (4.5-8 Hz), alpha (8.5-13 Hz), and gamma (30-45 Hz), with a predominant power in the beta/gamma range in the active waking state. It is also known that this signal contains a 60 Hz power line interference component. Higher frequencies in the EEG frequency spectrum area are also present but are known to be related to motion artifacts, ocular-motor activity, as well as other noise sources. Using your knowledge of signal processing, identify: a) Would anti-aliasing filtering be required? If so, what would you set your cutoff frequency to be? Justify your answer. b) Select the appropriate sampling frequency for this signal, such that both the frequency and time domain representations of the digital signal are accurate. c) If you choose to process only 10 seconds worth of data, what is the resulting frequency resolution?

Explanation / Answer

If you sample the EEG Signal at around 400Hz , then anti-aliasing filter would not be required. Because the maximum frequency component in EEG Signal can be around 100 to 200 Hz, But then 400 Hz sampling would generate lot of samples,will cause storage issues for a long time duration signal. I think It would be better to use a anti-aliasing filter at around 50 Hz cutoff frequency, In that way 120 Hz sampling would suffice, and you would get all - theta, alpha and gamma frequencies. b.) Sampling frequency of 120- 150 Hz would suffice, however for a very accurate time domain representation 500 or even 1 KHz sampling rates would be appropriate.It depends on how precise you want your signal to be in time domain. c.) For a sampling rate of 500 Hz, 10s generates 5000 samples. Thus 5000 points in DFT of the signal. Frequency resolution would be 50 Hz/50000 = 0.01 Hz For fs=150 Hz, resolution would be 0.033 Hz. both are fine I guess Depending upon data volume you want, sampling rate can be adjusted.

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